1. Field of the Invention
This invention relates to an improvement in a method for forming integrated circuit structures. More particularly, this invention relates to improvements in the method of forming a trench in an integrated circuit structure to separate one or more devices therein from other portions of the structure.
2. Background Art
In the formation of an integrated circuit structure, it is sometimes desirable to electrically separate or insulate one or more devices from adjacent portions of the structure by etching a slot or trench in one or more layers of the structure, usually in a silicon layer. After formation of the trench, a layer of silicon oxide is deposited or grown on the exposed surface to provide the desired electrical insulation or dielectric. However, for purposes of subsequent planarization, the groove or trench must be refilled. Conventionally, this is accomplished by depositing a layer of polysilicon followed by etching back or polishing of the surface to achieve the desired planarization.
In the normal practice of forming such a trench, conventional anisotropic etching is carried out through a mask or pattern of silicon dioxide (silox) which is placed over the silicon layer to be etched, resulting in the formation of a narrow trench having the same width as the mask. This trench will sometimes be formed somewhat bowed, i.e., it will tend to neck in at the upper corners. This, in turn, may result in the formation of a void during subsequent deposition of the polysilicon filler as shown in FIG. 1 representing the prior art.
Etching and/or polishing during subsequent planarization processing steps may open this void since it normally forms just beneath the corners, i.e., just beneath the necked down portion. Thereafter, oxidation of the planarized surface will result in undesirable oxidation of the now exposed polysilicon surfaces in the void. This oxidation, in turn, creates undesirable internal stresses due to the expanded volume of the silicon dioxide as it forms upon opposing walls of the void.
Modification of the trench profile to prevent the formation of such voids has been unsuccessful. Since, apparently, the process cannot be carried out in a manner which will prevent such formation of voids, it would be highly desirable to prevent any voids in polysilicon which do occur within the trench, as it is planarized, from being subsequently opened and exposed to undesirable oxidation.